If you’ve ever spotted bright orange patches on the rind of a cheese, there’s a good chance it was Sporendonema casei. While orange may instill a sense a fear, this orange mold isn’t out to get you. It’s a benign mold species that contributes unique aesthetics and flavors in cheese rind ecosystems.
Sporendonema casei is one of two species in the fungal genus Sporendonema. The other species, Sporendonema purpurascens, is equally eccentric with it’s purple color and sometimes contaminates mushroom growing facilities.
Macro- and microscopic appearance:
The mycelium of this fungus is very slow-growing and is initially white (see photo below). As the fungus grows, it produces spores that create its orange color. In ideal conditions in the lab, this can take several weeks.
Orange patches are made up of mycelia that segment to form conidia (or spores) as shown below. This method of asexual reproduction is different from spore production in many other molds, such as Penicillium, which form spores on distinct structures called conidiophores.
This mold is only found on the rinds of cheeses. According to recent work in France, it has never been found outside of the dairy environment. The fungus generally occurs after other fungi have colonized the cheese surface, although it has been observed growing on relatively young wheels of cheese. It is found on both European and North American natural rind cheeses.
It is important to note that Sporendonema casei does not cause the orange coloration of washed rind cheeses. Those cheeses get their orange colors from other bacteria, yeast, and molds.
Sporendonema casei, as with many naturally occurring cheese molds, has not been very well studied, so we know little about what it actually does to the cheese. Brian Ralph, the cave manager for Murray’s in New York City, has developed an aging technique where he inoculates Hudson Flower with Sporendonema casei. Brian notes that these cheeses have a deeper mushroom note compared to similar cheeses lacking the Sporendonema casei.
As far as we are aware, this fungus has never been reported to cause food-borne illness, infections, or produce mycotoxins, although there has not been a comprehensive assessment of the safety of this fungus.
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